The inventive concept relates to optical receivers and, more particularly, to multi-channel optical receiving modules.
The amount of data transmitted through a network increases recently, such that a wavelength division multiplexing (WDM) technique is applied to an optical transmission system using a single-channel. In the WDM technique, data having various wavelength bands may be multiplexed or de-multiplexed and then may be transmitted and/or received through one optical fiber.
Thus, a multi-channel optical transmitting/receiving module may be required in an optical transmitting/receiving system applied with an multi-functional, high integrated and optical sub-module platform for a network based on the WDM technique. The multi-channel optical transmitting/receiving module may be a multi-channel transmitter optical sub-assembly (TOSA), a multi-channel receiver optical sub-assembly (ROSA), or a multi-channel optical sub-assembly (OSA).
Recently, the development of the multi-channel ROSA being a high sensitive optical receiving component has been demanded in a metro access network system requiring massive data transmission as a transmission distance increases. A photodiode (PD) having a high sensitive characteristic should be used for manufacturing the high sensitive ROSA. However, the high sensitive ROSA including the PD may be more difficult to fabricate, as compared with a ROSA including a general PIN photodetector.
A multi-channel optical receiving module may convert optical signals inputted in parallel through a de-multiplexer physically connected to an optical fiber into electrical signals and then may receive data transmitted by the optical signals. A passive alignment process or an active alignment process may be performed on optical devices (e.g., an optical fiber coupler, an optical de-multiplexer, and an optical signal receiver) in order to minimize loss of light generated from an optical signal generating device. In the passive alignment process, the optical devices are aligned with and then fixed at predetermined positions of a substrate. In the active alignment process, distances between the optical devices and a position where a power of the received optical signal is maximum may be determined in due consideration of the intensity of the optical signal, a beam pattern, a receiving mode of a receiving device and a receiving efficiency by an additional alignment apparatus, a laser welding apparatus, or a handwork system. The active alignment process may be performed in order to maximize an efficiency of the received signal.
The passive alignment process may simplify the alignment between the optical devices and packaging of the optical devices. However, the passive alignment process may deteriorate accuracy and reliability of the optical devices. The active alignment process should control optical powers, beam patterns, and receiving efficiencies of the optical devices, such that a processing time and a process cost may increase.
Optical connection techniques have been developed for manufacture of the multi-channel optical receiving module. For example, optical coupling methods within the optical receiving module may include a first method of directly coupling the light receiving device to a ribbon optical fiber multi-channel connector having a reflecting mirror disposed at an inclination angle of 45 degrees; a second method of coupling the light receiving device to a polymer optical waveguide having a reflecting mirror disposed at an inclination angle of 45 degrees and of connecting the polymer optical waveguide to a multi-channel optical connector; a third method of vertically coupling the light receiving device to a polymer optical waveguide and of connecting the polymer optical waveguide to a multi-channel optical connector; or a fourth method of vertically coupling the light receiving device fixed on a plastic package to a multi-channel optical connector. The light receiving device (i.e., the photodetector) may use a photodiode array.
According to the second method, the reflecting mirror may be easily formed, and an optical coupler, an optical switcher, and a WDM device may be built into the polymer optical waveguide. Thus, function expansion of the entire module may be easily realized. However, if the module having the two-dimensional optical coupling structure is applied to a parallel connection optical receiving module having an expanded function, a great coupling loss may be caused by a distance difference between the optical fiber and the photodetector. Thus, a desired efficiency may not be obtained from the optical receiving module.